A woman walks past the entrance for the Darwin's Evolution Exhibition in the Calouste Gulbenkina Foundation in Lisbon February 12, 2009. The exhibition, which will be opened to the public on Friday, runs till May and more than 100,000 visitors are expected, according to the organizers. REUTERS/Jose Manuel Ribeiro

A pair of University of Michigan biologists say they found evidence that contradicts one of the fundamental laws of evolution.

Findings published in the Proceedings of the National Academy of Science journal, by biologists Pavel Klimov and Barry O'Connor indicate evolution is not a one way road. During a study focused on the evolution of free-living house dust mites, the duo found evidence that challenges Dollo's Law which stipulates that once an organism evolves and assumes certain features it cannot drop them and adopt the form of its ancestors.

Researchers analyzed DNA from more than 700 different mite species and tested 62 different hypotheses about their evolution. Their findings suggest dust mites have forgone the parasitic lifestyle of their ancestors who depended on their host and instead have become free-feeding organisms that dine on such things as discarded human skin. Parasitic dust mites are believed to have evolved from free-living organisms.

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"Parasites can quickly evolve highly sophisticated mechanisms for host exploitation and can lose their ability to function away from the host body," Klimov said in a statement, International Business Times reports.. "They often experience degradation or loss of many genes because their functions are no longer required in a rich environment where hosts provide both living space and nutrients. Many researchers in the field perceive such specialization as evolutionarily irreversible."

The parasitic characteristics of their ancestors may have helped dust mites make the transition to becoming free-living organism. Researchers believe that dust mites developed a powerful digestive system from their parasitic forebears that allows them to eat things like discarded human nails and skin.

A possible factor that contributed to dust mites' unusual evolutionary path may have been that their parasitic ancestors often switched between different animal hosts, forcing them to survive while searching for a host.